[Enhancement] Consolidate DSLX frontend flags into common library

### What's hard to do? (limit 100 words)

We have a number of DSLX utilities that need flags like `dslx_stdlib_path` and `warnings_as_errors`, etc.

Cursory list:

* interpreter_main
* eval_ir_main
* prove_quickcheck_main
* ir_converter_main
* cpp_transpiler_main
* https://github.com/google/xls/pull/2474

These all independently specify the set of flags, which might not even be exactly the same (Related: #2365).

### Current best alternative workaround (limit 100 words)

Copy/paste relevant flags from an existing binary like `interpreter_main`.

### Your view of the "best case XLS enhancement" (limit 100 words)

In codegen, XLS has [codegen_flags.proto](https://github.com/google/xls/blob/c4afeb0bf89eb0289a3a4835fd436b056a64e345/xls/tools/codegen_flags.proto) and [scheduling_options_flags.proto](https://github.com/google/xls/blob/c4afeb0bf89eb0289a3a4835fd436b056a64e345/xls/tools/scheduling_options_flags.proto) that can be shared across drivers.

Something similar might be desirable for the frontend.